In the prior art, there has been known the attenuator device utilizing the offset-dispersion double spectrograph. This offset-dispersion double spectrograph may also be called the offset-dispersion type double monochromator or the zero dispersion double spectrograph. In the attenuator device utilizing the offset-dispersion double spectrograph, an input beam is sequentially subjected to two wavelength dispersion effects (in the opposite directions), the diffracted beam after receiving the first wavelength dispersion effect and before receiving the second wavelength dispersion effect is subjected to an attenuation operation. Then, the attenuated beam is subjected to the second wavelength dispersion effect and is then output to the outside.
In the attenuator device utilizing the offset-dispersion double spectrograph, as described in JP-A-2002-196173, the attenuation operation is executed by using a micro mirror array. Specifically, the micro mirror array is so configured that the diameters of the individual micro mirrors may be smaller than the spot diameter of beam (to be operated) incident on the micro mirror array, and that the multiple micro mirrors may be arranged in the spot diameter of the beam to be operated. Moreover, the attenuation operations is performed by inclining some of the plural micro mirrors positioned in the spot diameters in directions different from the output direction and by guiding to outside of the optical path, i.e., discarding a part of the beam to be operated. Moreover, the beam discarded at that time is detected by a sensor to monitor the spectral information, so that the number of micro mirrors to be inclined in the directions different from the output direction is controlled on the basis of that spectral information.
In the attenuator device utilizing the offset-dispersion double spectrograph described in JPA-2002-196173, the micro mirror array is so configured that the diameter of the individual micro mirrors may be smaller than the spot diameter of the beam (to be operated) incident on the micro mirror array, and that the multiple micro mirrors may be arranged in the spot diameter of the beam to be operated. This arrangement raises a problem that the configuration of the micro mirror array is complicated.
Moreover, the arrangement imagines the single output port so that it cannot meet the function using the plural output ports selectively.